The present invention relates, in general, to semiconductor devices and, more particularly, to quantum well semiconductor structures having a single source for both n-type and p-type doping.
Traditional semiconductor devices are formed on a semiconductor substrate. Intrinsic semiconductor material is very high resistivity or semi-insulating. Conventionally, the resistivity of semiconductor material is lowered by doping portions of the semiconductor material with atoms that provide excess electrons and holes. For example boron is a P-type dopant in silicon, while phosphorous and arsenic are N-type dopants. This type of doping is called extrinsic doping.
One problem with extrinsic doping is that the dopant atoms increase scattering of charge carriers moving in the semiconductor material. Increased scattering is reflected in lower mobility in the semiconductor material. Moreover, lower mobility results in devices with slower switching and higher power consumption. This problem is addressed to some degree by modulation doping in heterostructure semiconductor devices. Modulation doping physically separates the dopant atoms from the excess charge carriers that they provide using quantum wells and barriers.
Another problem with conventional extrinsic as well as modulation doping is that one kind of atom is required for N-type doping and another kind of atom is required for P-type doping. To manufacture bipolar devices, which are devices having both N-type and P-type regions, both kinds of doping atoms must be supplied. This increases capital requirements for manufacturers and complicates processing. Because many of the dopant atoms used in semiconductor processing are toxic, manufacturing safety is directly affected by the number of chemicals and dopants required to produce a device.
What is needed is a semiconductor structure that provides both N-type and P-type doping from a single dopant source and that is compatible with modulation doping techniques.